The present invention relates to a method for drawing a desired circuit pattern using a charged particle beam and, more particularly, to a method of minimizing too-small figures remaining in integrated circuit patterns of semiconductor devices to be drawn on an object or a workpiece such as a mask and a wafer.
Recently, chip circuit patterns are increasingly micronized and complicated along with the increase in packing density of semiconductor devices such as a dynamic random access memory or a microprocessor. A charged particle beam pattern drawing system is generally used to draw circuit patterns of highly-integrated semiconductor devices on a workpiece such as a mask or a wafer. First, a chip circuit pattern is formed using a design tool such as a computer-aided design system (also known as a "CAD" system or simply referred to as "CAD"). The initially designed circuit pattern is drawn or depicted on a workpiece using the charged particle beam pattern drawing system.
Generally, graphic data of a chip circuit pattern created by a CAD system cannot be directly used as input drawing data of the charged particle beam pattern drawing system. This is because of the following facts:
(1) Unlike CAD design data which represents circuit pattern regions having various types of polygonal shapes, input graphic data of the charged particle beam pattern drawing system can only use basic rectangles having comparatively simple limited shapes such as a rectangle, a trapezoid, and a parallelogram in order to represent a circuit pattern region subjected to charged particle beam pattern drawing. Therefore, the circuit pattern must be divided into a combination of these basic rectangles.
(2) If the divided circuit patterns to be subjected to charged particle beam pattern drawing include overlapping figures, the overlapping region is excessively exposed, thus degrading the beam pattern drawing precision.
Usually, in a system or a computer for generating data for the charged particle beam pattern drawing system, when a circuit pattern to be drawn is divided into several basic rectangles (unit figures), such unit figures often include a figure having a side shorter than a length (minimum allowable length) allowable as a side of a unit figure of pattern drawing (to be referred to as a "too-small figure" hereinafter). If a too-small figure is directly drawn on a workpiece with a charged particle beam, the current density of the irradiated charged particle beam is smaller than that in other ordinary unit figures. As a result, the beam radiation amount for the too-small figure on the workpiece is insufficient to cause a defect in pattern drawing such as a pattern disconnection and/or pattern extinguishment, thus considerably degrading the quality of the resultant drawn pattern. In order to draw a pattern of a satisfactory high quality, it has been desired in this field that remaining of the too-small figures as described above be suppressed or prevented in divided unit figures of an input pattern.